Demos: 1J-15 Unstable Block

A large block has a massive (visible) metal slug embedded near one end, placing the center of gravity of the block near that end. The block is placed on a ramp that can be raised through a measured angle. Rubber on the block and ramp prevents slipping. The block will be stable against tipping as long as a vertical line passing through the center of gravity does not intersect the plane beyond the edge of the block. When the block is placed with the weighted end down, the plane can be lifted to a much higher angle (see Figure A). When the block is reversed, the the plane angle has to be much smaller to prevent tipping (Figure B).

Directions: Tape the rubber mat to the plane surface. Place the block on the plane with the weighted end lower and higher, respectively. Loosen the screw and lift the plane upward slowly and note the angle at which it first starts to tip.

Suggestions for Presentation: Ask students what it means for objects to have a high or low center of gravity. What are the practical aspects of this. Ask which orientation of the block will likely tip first. Most students will guess correctly that it is the situation shown in Figure B, but might not be able tell you why. Can they predict at what point the block will start to tip?

Applications: Objects with higher centers of gravity and narrower bases are more prone to tip. Apply this to the design of race cars, for example. Why are SUVs more prone to tipping than regular cars?